Research On Control Strategy Of Aviation Single Phase Flying Capacitor High Power Factor Rectifier

In order to meet the electrical standard of aviation AC power supply system equipment,match the power demand of secondary DC load,and further demand for aviation power efficiency and volume miniaturization,a five level flying capacitor totem pole bridgeless PFC topology based on GaN switch is selected as the research object,and its main advantages,operating characteristics,control strategy and the balance problem of flying capacitor voltage are studied.The basic working principle and PFC control strategy of the flying capacitor PFC rectifier are studied.Firstly,the basic implementation and advantages of Flying Capacitor Multi-level(FCML)technology with carrier phase shift modulation are analyzed,and the parameters of the converter are designed based on the circuit mode analysis under different conditions.Based on the analysis of the desired modulation waveform corresponding to the AC side chopping voltage,a inner current loop deadbeat PFC control strategy for the converter is presented.Voltage balance of flying capacitor is an important condition for stable and efficient operation of flying capacitor PFC converter.The charging and discharging characteristics of flying capacitor under ideal open-loop condition are analyzed,and the mechanism of voltage balance of flying capacitor through deadbeat PFC control strategy is studied.In view of the high requirements of sensing accuracy and digital control bandwidth when using this control strategy to realize the voltage balance of flying capacitor,based on the analysis of the natural balancing of flying capacitor voltage of PFC rectifier,a passive voltage balance method of flying capacitor is proposed.The mismatch of switching delay which affects the voltage balance of flying capacitor is studied.The influence mechanism of switch delay mismatch on the voltage balance of flying capacitor is analyzed,and the function performance of different switch combinations with additional delay time on the charging and discharging of flying capacitor is further discussed.Finally,based on the hardware driving circuit,the factors that may lead to the switch delay deviation are analyzed.Combined with the characteristics of GaN driving,a driving scheme of switchs on flying capacitor bridge leg is proposed to reduce the switch delay mismatch.In the basis of the aforementioned theoretical research and simulation experiments,an experimental platform based on digital control is built to verify the theoretical analysis and control strategies.